The present invention relates to a method of depositing a thin film of a diamond-like form of carbon on the surface of a substrate.
There is continuing interest in the formation of diamond-like films as protective coatings on substrates such as lens and other optical elements. These films are attractive by virture of their inherent physical properties of hardness, inertness, transparency and high refractive index.
One method of depositing a diamond-like film on a substrate is described by S. Aisenberg in his U.S. Pat. No. 3,904,505 issued Sept. 9, 1975. This method employs a technique, generally referred to as ion beam deposition, wherein an energetic beam of carbon ions is created and extracted into a low pressure deposition chamber and accelerated to the surface of the substrate. Precise identification of the films produced by the Aisenberg method has not been reported. It is theorized that the film is heterogeneous, being made up of the several linear forms of allotropic carbon now generically referred to as carbynes. It can be said, in general, that of all known processes for producing diamond-like or carbyne films none results in a film of a selected one of the carbynes, but rather all such films are formed without control on the specific carbyne content.
In my prior work reported in the literature, it was noted that high temperature carbon gas when quenched on the surface of a cool substrate forms a silvery deposit. This deposit included an abundance of the carbyne known as chaoite and also several of the other carbynes. In my prior U.S. Pat. No. 3,733,394, issued May 15, 1973, a similar silvery deposit of chaoite was deposited on the surface of a heated graphite rod. My prior work however did not recognize that by closely controlling the temperature range of the carbon gas at which it was quenched, a single specie of the carbynes would be formed. In addition to the carbynes there were undoubtedly present in these deposits other forms of carbon including glassy carbon and graphite.